Lens modules, especially autofocus lens modules, have a lens holder to which is mounted a single lens or lens assembly, simply referred to herein as a lens, for focussing an image onto an image plane. In use, the image plane would be an image sensor such as a CMOS or CCD device but in practice, the lens module is produced bare, meaning without the lens and without the image sensor which are fitted by the camera module maker. The lens module has a lens holder which is arranged to be driven by an actuator along a short straight path. Known actuators include DC motors, stepping motors, voice coil motors, ultrasonic motors and electrostrictive actuators including piezoelectric actuators.
There is a strong demand for small lens modules as small camera modules are being incorporated into more devices such as mobile phones and laptop computers and computer monitors. At the same time, the desire is for lower price and smaller size.
Voice coil motor driven lens modules have an advantage in price and as the size is reduced, provides satisfactory performance over a limited range of motion. Recent developments are shown, for example, in Japanese Patent Applications JP 2006-58662 and JP 2005-128405 by Shicoh Engineering Company Ltd.
One problem with current voice coil motor driven modules is that it is difficult to further reduce the overall size of the module, yet maintain the lens size and still improve the performance, in particular, the response time of the module to achieve focus from a resting position.
Another problem with small lens modules is that the lens is not securely mounted within the module and can be damaged due to shocks received by dropping the module or from operating in high or severe vibration conditions.